Housing, housing system, electrolytic capacitor comprising said housing, and electrolytic capacitor system

ABSTRACT

The invention relates to a housing ( 1 ) comprising an electrically conductive cup ( 2 ), which comprises a wall ( 3 ) and a bottom ( 4 ), and an electrically insulating envelope ( 5 ), which covers the exterior of the cup ( 2 ) and features an opening ( 6 ) on the bottom side that is smaller than the bottom ( 4 ) of the cup ( 2 ), and a fill element ( 7 ), which is effectively heat-conductive and is disposed within the opening ( 6 ), and a cover element ( 8 ), which is electrically insulating and covers the bottom ( 4 ) of the cup ( 2 ) and overlaps the envelope ( 5 ). Furthermore, the invention relates to an electrolytic capacitor comprising a rounded coil ( 10 ) and the housing ( 1 ), as well as a housing structure and a structure comprising an electrolytic capacitor. Through the use of a flat cup bottom in connection with a fill element ( 7 ) and a cover element ( 8 ), improved heat dissipation from the housing ( 1 ) can be achieved, as well as a reduction in the cost of manufacturing the cup ( 2 ).

[0001] The invention relates to a housing comprising an electricallyconductive cup having a wall, a bottom, and an electrically insulatingenvelope. The electrically insulating envelope covers an exterior of thecup and features an opening on a bottom of the cup that is smaller thanthe bottom of the cup. The invention also relates to a structure of thehousing, an electrolytic capacitor, and a structure of the electrolyticcapacitor.

[0002] Conventional housings that may be used for electrolyticcapacitors are typically made of aluminum. Electrolytic capacitors areattached to printed circuit boards, either individually or in batteries.Because the potential of an anode or a cathode of a capacitor isnormally applied to an aluminum housing of the capacitor, the housingmust be electrically insulated toward its exterior. In particular, ahousing whose bottom is attached to a printed circuit board must beelectrically insulated vis-à-vis the printed circuit board. Thiselectrical insulation is achieved via an insulating envelope.

[0003] When high current is applied to an aluminum electrolyticcapacitor, heat is generated that must be dissipated to its exterior.Improved heat dissipation from the capacitor increases the maximumcurrent carrying capacity of the capacitor. Consequently, in capacitorbatteries, for example, the number of capacitors in a battery can bereduced without changing the overall current carrying capacity of thebattery.

[0004] Housings are known that are insulated on their bottoms. Inparticular, the bottom of a housing cup may be insulated via a plasticdisk made, for example, of PVC. The housing is subsequently encased witha heat-shrinkable sleeve. This heat-shrinkable sleeve corresponds to theelectrically insulating envelope of the cup. When such a cup is mountedon a printed circuit board, a planar air gap is created at the bottom ofthe cup. The planar air gap is a very poor heat conductor and,therefore, impairs heat dissipation from the housing through the printedcircuit board. The plastic disk disposed on the bottom of the cup isalso a poor heat conductor.

[0005] Heat dissipation from a housing through the bottom of a cup canbe improved by the structured described in DE 296 17 888 U1. Accordingto this document, the bottom of the cup includes a step that forms acentrally disposed elevation that is smaller than the cup diameter. Thecup is encased in a heat-shrinkable sleeve up to this step, and is theninsulated with a thermally conductive foil that covers the entiresurface of the bottom.

[0006] However, because the cup is an extruded aluminum part, the stepbottom is formed as a solid piece. As a result, a large quantity ofaluminum material is needed to produce the cup. The use of this cup as ahousing for aluminum electrolytic capacitors is also disadvantageoussince a solid cup bottom provides poor control over gas developmentduring operation of the capacitor and resulting pressure-relateddeformation of the cup. As a result, the solid cup bottom can create abulge and thereby create air gaps over a large surface area. These airgaps poorly dissipate heat and cannot be offset by the thermallyconductive foil on the bottom of the cup.

[0007] Another disadvantage of known housings is that when theheat-shrinkable sleeve is applied, the sleeve must be prevented fromcovering the step. This is because the step bottom determines the finaldimensions of the heat-shrinkable sleeve and it is very difficult toconform to fixed heat-shrinkable sleeve dimensions, particularly thoseof the segment oriented toward the center of the housing. The sleeve isprevented from covering the step using a complicated heat-shrinkingprocess.

[0008] Therefore, an objective of the present invention is to provide ahousing that features effective electrical insulation and effective heatdissipation on its bottom, and that can be easily manufactured.

[0009] According to the invention, this objective is achieved with ahousing pursuant to claim 1. Additional embodiments of the invention, ahousing structure, an electrolytic capacitor with the housing, and astructure of the electrolytic capacitor, are disclosed in the remainingclaims.

[0010] The invention is directed to a housing with an electricallyconductive cup. The invention comprises a wall, a bottom, and anelectrically insulating envelope. The envelope covers the exterior ofthe cup and features an opening on a bottom of the cup that is smallerthan the bottom of the cup. A fill element that effectively conductsheat is disposed inside the opening. A covering element, which iselectrically insulating, covers the bottom of the cup and overlaps theenvelope.

[0011] Because of the fill element disposed on the bottom which conductsheat well, or because of the covering element which is electricallyinsulating, the housing of the invention features, on its bottom, botheffective heat conductance and effective electrical insulation. Becausethe opening created on the bottom as a result of the electricallyinsulating envelope is filled with the fill element, a step bottom inthe cup is not needed. Thus, advantageously, the housing of theinvention can be equipped with a cup with a flat bottom that can bemanufactured as an extruded part inexpensively and using relativelylittle material. As a result of the fill element, an air gap between thebottom of the housing and a printed circuit board supporting the housingis at least considerably reduced if not entirely eliminated.

[0012] Moreover, because the fill element can be disposed at any pointon the cup bottom, the configuration of the electrically conductiveenvelope and, in particular, the position of the opening can be flexiblyselected. This is particularly advantageous with poorly controllableprocesses for manufacturing a suitable electrically insulating envelope,such as heat-shrinkable sleeves.

[0013] Furthermore, because the cover element overlaps with the envelopeof the cup, effective electrical insulation is provided between thehousing bottom and a printed circuit board. The overlap between thecover element and the envelope creates a long creep path, which must beovercome by electrical surface currents.

[0014] The housing is therefore especially suitable for a housingstructure in which the entire surface of the bottom of the cup of thehousing is pressed against a substrate surface. This is also an objectof the invention. As a result of planar contact between the bottom andthe substrate surface, the heat created in the housing during operationof, e.g., an electric element disposed therein, can be effectivelytransferred to the substrate surface and, therefore, to the substratefor further dissipation.

[0015] In this arrangement, the fill element can be designed to beelastically ductile, which is especially advantageous if the housing isto be designed to be mounted onto a substrate surface, which providesfor the cup bottom being pressed onto the substrate surface. As a resultof the pressure being applied or because of deformation of the cup as aresult of elevated pressure inside the cup, an elastically ductile fillelement can compensate for any remaining air gaps. This effect can beamplified even further if the cover element is also designed to beelastically ductile.

[0016] Moreover, to further reduce the size of the air gap, caused bythe opening in the electrically insulating envelope, between the housingand a substrate surface disposed beneath it, it is advantageous if thefill element fills at least 80% of the area of the opening. Heatdissipation from the housing can be effectively improved as a result. Toobtain the best possible heat dissipation from the housing, it is alsoadvantageous if the fill element is executed in the shape of a disk, thethickness of which deviates from the thickness of the envelope by lessthan 10%. This allows the bottom of the housing to be kept as flat aspossible, which allows additional air gaps to be reduced.

[0017] The fill element can be, e.g., a braided metal material. Theadvantage of braided metal materials is that they are elasticallyductile and are effective heat conductors.

[0018] However, the fill element can also be designed to be electricallyinsulating. In this case, in addition to providing effective heatconductance, the fill element fulfills the additional function ofelectrically insulating the cup bottom. Thermally conductive foil is anexample of a material that can be used as a material for such a fillelement. Thermally conductive foils are produced using silicon, forexample, and are filled with ceramic material. For example, siliconrubber filled with bornitrit is known under the product names Sil-Pad orGAP-Pad, which are sold by the Bergquist Company. Suitable thermallyconductive foils are also commercially available under the generic nameof thermal silicon foils.

[0019] Thermally conductive foils, such as those described above, areadvantageous in that they are elastically ductile, effective heatconductors, and electrically insulating. Since a fill element made withsuch a foil combines three functions into one element, its use is highlyadvantageous.

[0020] Effective electrical insulation of the housing can be achieved bydesigning the cover element in such a way that it covers the entiresurface of the bottom of the cup. This results in the greatest possibleoverlap with the envelope and a maximum creep path for surface currents.These features improve the electrical insulation of the housing.

[0021] Depending on the application, the cover element can also featurean overlap relative to the bottom of the cup. The cover element can be,e.g., a foil made of polyester or polyvinylchloride. The advantage ofthese materials is that they are inexpensive to manufacture, areelastically ductile, and are effective insulators for electricallyinsulating the housing.

[0022] However, the cover element can also be designed to be effectivelyelectrically insulating, which improves heat dissipation from thehousing even further. A cover element made of a thermally conductivefoil, as described above, is particularly suitable for this purpose.

[0023] Another advantageous embodiment of the invention is achieved bymaking the fill element and the cover element integral parts of a singleinsulating part, which exhibits effective thermally conductiveproperties and is, at the same time, electrically insulating. Thisreduces the number of parts needed to manufacture the housing. Theinsulating part can be made of a thermally conductive foil designed as agraduated part, the shape of which can be created by placing a fillelement and a cover element on top of one another.

[0024] The electrically insulating envelope of the cup can be aheat-shrinkable sleeve that is shrink-wrapped onto the cup. Suchshrink-wrapping of the cup with a heat-shrinkable sleeve is veryinexpensive, fast, and easily achieved with simple means. However, thesize of the opening on the bottom is very difficult to control withstandard heat-shrinkable sleeve materials. For this reason, when aheat-shrinkable sleeve is used, the heat-shrinkable sleeve can beapplied over only part of the cup bottom, depending on the desiredoverlap and, therefore, electrical insulation of the housing bottom.Subsequently, the remaining opening in the cup bottom can be filled witha suitably dimensioned fill element. Thus, in contrast to the use of astep bottom, the desired electrical insulation can be freely selectedwithin wide limits, though at the cost of heat dissipation.

[0025] Advantageously, the cup of the housing can be produced viaextrusion. The manufacturing process is inexpensive and easily andquickly executed, even for large numbers of units. Aluminum, forexample, can be used as a conventional material for the cupsmanufactured by extrusion. Such an aluminum cup is ideally suited as ahousing for an aluminum electrolytic capacitor in which a rounded coilis disposed in the interior of the cup. Such a capacitor is anadditional object of the invention.

[0026] The use of the housing of the invention in an electrolyticcapacitor is also advantageous in that gases produced during operationof an aluminum electrolytic capacitor and/or resulting pressure andassociated deformation of the housing can be effectively offset bycombining an elastic fill element with an elastic cover element.

[0027] Advantageously, such a capacitor can be attached to a flatsubstrate in a structure of the invention, wherein the bottom of the cupof the housing is two-dimensionally pressed onto the substrate surface.This creates advantages in terms of thermal contact between thecapacitor housing and the substrate because, in the case of acylindrical cup with a flat bottom, which is best suited forelectrolytic capacitors with rounded coils, a maximum contact surface isachieved. In contrast, attaching the cup to the substrate by placing thecup onto the substrate would only establish a very small contactsurface.

[0028] The following explains the invention in greater detail on thebasis of exemplary embodiments and the corresponding figures.

[0029]FIG. 1 depicts, by way of example, an inventive electrolyticcapacitor structure with the inventive housing on a substrate.

[0030]FIG. 2 depicts, by way of example, a cross-sectional view of thehousing, in which the fill element and cover element are integrated intoan insulating element, and in which the envelope is disposed between thebottom of the cup and the cover element.

[0031]FIG. 3 depicts a housing pursuant to FIG. 2, in which the coverelement is disposed between the envelope and the bottom of the cup.

[0032]FIG. 4 depicts, by way of example, a cross-sectional view of thehousing, in which the fill element and cover element are separate parts,and in which the cover element is disposed between the envelope and thebottom of the cup.

[0033]FIG. 1 depicts an inventive housing structure with a housing 1.Housing 1 comprises a cup 2, in which a rounded coil 10 of an aluminumelectrolytic capacitor is disposed. Cup 2 features a wall 3 and a flatbottom 4. Cup 4 is encased within an envelope 5, which is electricallyinsulating and which can be, e.g., a heat-shrinkable sleeve. Envelope 5covers wall 3 and at least partially covers bottom 4 of cup 2.

[0034] Envelope 5 features an opening 6 on its bottom side, whichopening 6 is smaller than bottom 4 of cup 2. A fill element 7 that canbe, e.g., a braided metal material or a thermally conductive foil, isdisposed in opening 6. Fill element 7 can be applied followingapplication of envelope 5 to cup 2. If fill element 7 is a thermallyconductive foil, the thermally conductive foil can be self-adhesive.Alternatively, the thermally conductive foil can also be glued to bottom4 of cup 2.

[0035] On its bottom, housing 1 is covered with a cover element 8, whichcan be thermally conductive foil. The thermally conductive foil can beself-adhesive or it can be glued to fill element 7 and/or envelope 5.

[0036] Housing 1 is attached to a substrate 9 via a fastening element11. Such attachment corresponds to mounting of an aluminum electrolyticcapacitor onto a printed circuit board. Fastening element 11 is onlydepicted schematically and can be implemented as, e.g., a clip, as isknown in the art, which is stretched around wall 3 of cup 2 and which isscrewed to substrate 9.

[0037] Using fastening element 11, tensioning of bottom 4 of cup 2 onsubstrate 9 can also be achieved. This tensioning can result inadditional reduction in air gaps, while at the same time improvingthermal contact between housing 1 and substrate 9.

[0038] If cup 2 is cylindrical, the arrangement of housing 1 onsubstrate 9 depicted in FIG. 1 provides, as a result of planar mountingof bottom 4 of cup 2, a maximum possible contact surface between housing1 and substrate 9. This arrangement provides effective heat dissipationfrom housing 1 to substrate 9.

[0039]FIG. 2 depicts a housing 1, which is similar to that depicted inFIG. 1, except that fill element 7 and cover element 8 are integralparts of an insulating element 12. Insulating element 12 is a thermallyconductive foil with a step. According to FIG. 2, cup 2 can first beprovided with envelope 5. Envelope 5 can be shrink-wrapped onto cup 2,after which insulating element 12 can be secured by gluing in opening 6of insulating envelope 5. However, the reverse sequence is alsopossible; i.e., in which insulating element 12, as depicted in FIG. 3,is fastened to bottom 4 of cup 2 and subsequently is covered withenvelope 5, such as a heat-shrinkable sleeve.

[0040] According to FIG. 4, cover element 8, which can be a separatepart, can also be fastened first to bottom 4 of cup 2. Envelope 5, whichmay be a heat-shrinkable sleeve, can then be applied. Finally, opening6, which is formed by envelope 5, can be filled using fill element 7.

[0041] The invention is not limited to the exemplary embodimentsdescribed herein. Instead, it is defined in its most general form byclaim 1.

1. Housing (1) comprising an electrically conductive cup (2), whichcomprises a wall (3) and a bottom (4); an electrically insulatingenvelope (5), which covers the exterior of the cup (2) and whichfeatures, on the bottom side, an opening (6), which is smaller than thebottom (4) of the cup (2); a fill element (7), which is effectivelyheat-conductive and is disposed inside the opening (6); a cover element(8), which is electrically insulating, that covers the bottom (4) of thecup (2) and overlaps the envelope (5).
 2. Housing according to claim 1,in which the fill element (7) is elastically ductile.
 3. Housingaccording to claim 2, in which the fill element (7) is executed in theshape of a disk, the thickness of which deviates from the thickness ofthe envelope (5) by less than 10%.
 4. Housing according to claims 1through 3, in which the fill element (7) fills at least 80% of the areaof the opening.
 5. Housing according to claims 1 through 4, in which thefill element (7) is a braided metal material.
 6. Housing according toclaims 1 through 4, in which the fill element (7) is electricallyinsulating.
 7. Housing according to claim 6, in which the fill element(7) is a thermally conductive foil.
 8. Housing according to claims 1through 7, in which the cover element (8) is elastically ductile. 9.Housing according to claims 1 through 8, in which the cover element (8)covers the entire surface of the bottom (4) of the cup (2).
 10. Housingaccording to claim 9, in which the cover element (8) overlaps the bottom(4) of the cup (2).
 11. Housing according to claims 1 through 10, inwhich the cover element (8) is a foil made of polyester orpolyvinylchloride.
 12. Housing according to claims 1 through 10, inwhich the cover element (8) is effectively heat-conductive.
 13. Housingaccording to claim 12, in which the cover element (8) is a thermallyconductive foil.
 14. Housing according to claims 6 and 12, in which thefill element (7) and the cover element (8) are integral parts of aninsulating element (12), which is effectively heat-conductive andelectrically insulating.
 15. Housing according to claim 14, in which theinsulating element (12) is a thermally conductive foil.
 16. Housingaccording to claims 1 through 15, in which the cover element (8) isdisposed between the envelope (5) and the bottom (4) of the cup (2). 17.Housing according to claims 1 through 15, in which the envelope (5) isdisposed between the bottom (4) of the cup (2) and the cover element(8).
 18. Housing according to claims 1 through 17, in which the envelope(5) is a heat-shrinkable sleeve, with which the cup (2) isshrink-wrapped.
 19. Housing according to claims 1 through 18, in whichthe cup (2) is manufactured by extrusion.
 20. Housing according toclaims 1 through 19, in which the cup (2) is cylindrical and features aflat bottom.
 21. Housing structure comprising a housing pursuant toclaims 1 through 20 and a flat substrate, in which the bottom (4) of thecup (2) of the housing (1) is two-dimensionally pressed onto the surfaceof the substrate (9).
 22. Electrolytic capacitor with a rounded coil anda housing pursuant to claims 1 through 20, in which the rounded coil(10) is disposed in the cup (2) of the housing (1).
 23. Structure of anelectrolytic capacitor pursuant to claim 22 on a flat substrate (9),wherein the bottom (4) of the cup (2) of the housing (1) istwo-dimensionally pressed onto the surface of the substrate (9).